1. Field of the Invention
This invention relates to a cable arranging structure that can suitably be applied to an electric signal transmission cable by way of which printed circuit boards transmit and receive electric signals in an electronic device.
2. Related Background Art
Electronic devices have been made to operate at increasingly high speed and perform excellently in recent years. As a result, however, there has been a problem that radiant noises of electronic devices adversely affect operations of other electronic devices. The adverse effects of radiant noises of electronic devices on other electronic devices are collectively referred to as EMI (electromagnetic interference). Such noises can give rise to operation errors of electronic devices. In view of this problem, a frequency band in which radiant noises are particularly serious is defined by law and the extent of noise radiation from an electronic device in this frequency band is rigorously controlled by regulations. Manufacturers of electronic devices are required to design products conforming to the regulations.
Radiant noises of electronic devices are generated by printed circuit boards and cables connecting printed circuit boards. Particularly, cables that are arranged to transmitting electric signals from a printed circuit board to another have become particularly serious sources of radiant noises as a result of the technological development of transmitting signals at high speed in recent years. Thus, it is a technological challenge how to effectively suppress radiant noises coming from cables.
Japanese Patent Application Laid-Open No. 6-3877 proposes a technique of covering a cable with an electrically conductive member in order to suppress radiant noises coming from the cable. According to Japanese Patent Application Laid-Open No. 6-3877, radiant noises are suppressed and prevented from affecting other loads by containing a cable (harness) that connects printed circuit boards in a duct made of an electrically conductive ferromagnetic material, e.g., a soft iron pipe, that is formed on the frame of a digital copying machine.
Japanese Patent Application Laid-Open No. 11-40900 proposes a cable arranging structure for tightly holding a cable (electrically conductive wires) close to a cabinet. The proposed technique is intended to suppress radiant noises even in the area where the cable is connected to a printed circuit board, particularly by deforming the electrically conductive surface of the printed circuit board, connecting it to the cabinet and arranging the cable close to the deformed surface.
However, in the case of a structure for arranging a cable in a duct as described in above cited Japanese Patent Application Laid-Open No. 6-3877, the cable and the electrically conductive surface are separated from each other by a large distance in the area where the cable is connected to the printed circuit board so that radiant noises are boosted rapidly in that area. Then, it is highly difficult to form a duct that entirely contains the cable including the parts where they are connected to printed circuit boards, although the difficulty may vary depending on the configuration of the electronic device and the arrangement of printed circuit boards. Particularly, preparation of a duct can be costly and require a large amount of work to be done when the duct has bent areas to show a complicated profile.
A structure for arranging a cable close to a cabinet as described in Japanese Patent Application Laid-Open No. 11-40900, on the other hand, essentially requires the cable to be warped and/or bent before it is arranged along the cabinet. Therefore, the technique is accompanied by a problem that an excessive load is applied onto the cable and the cable may not be able to be laid close to the cabinet depending on its structure. The problem of difficulty of laying a cable along the cabinet is very remarkable particularly when the distance separating two printed circuit boards is small. Additionally, the cable needs to be rigidly confined or anchored by some means or another so as to allow it to be constantly arranged close to the cabinet. These and other reasons make the structure very complex and costly. Furthermore, Japanese Patent Application Laid-Open No. 11-40900 describes an arrangement for laying a cable close to a cabinet by deforming the cabinet as shown in FIG. 7(B) of the patent document. Then, the cabinet needs to be previously processed for the deformation. Such an arrangement is not realistic because preparation of such a cabinet is costly and requires a large amount of work to be done.